1. Field of the Invention
The present invention relates to a musical tone synthesizing apparatus which simulates a tone-generation mechanism of a wind instrument so as to synthesize its sounds.
2. Prior Art
Recently, several kinds of musical tone synthesizing apparatuses, each of which synthesizes musical tones of a non-electronic musical instrument by use of a simulation model corresponding to its tone-generation mechanism, have been developed. This kind of technology is disclosed in, for example U.S. Pat. Nos. 4,984,276 and 4,130,043.
FIG. 15 shows a main portion of the conventional musical tone synthesizing apparatus which is designed to simulate the tone-generation mechanism of the wind instrument. In FIG. 15, 11 designates a non-linear circuit which is configured by a read-only memory (ROM) or a random-access memory (R) storing data corresponding to the predetermined non-linear function in form of the tables. In addition, 12 designates an adder, 13 designates a subtracter, while 14 and 15 designate multipliers. These circuit elements 11 to 15 are assembled together to configure a simulation model of which operations correspond to the mouthpiece and reed of the wind instrument such as the clarinet. In short, these circuit elements configure an excitation circuit 10.
Further, 20 designates a bi-directional transmission circuit which simulates the operations of the tube portion of the wind instrument, in other words, transmission characteristic of the resonance tube. This bi-directional transmission circuit 20 contains delay circuits D, Junctions JU, a low-pass filter LPF and a high-pass filter HPF. The delay circuits D simulate the propagation delay of the air-pressure wave propagated through the resonance tube; the Junctions JU are provided to be sandwiched by these delay circuits D; the low-pass filter LPF simulates an energy loss which is occurred when the air-pressure wave is reflected by the end terminal of the resonance tube; and the high-pass filter HPF cuts off the low-frequency component of the signal transmitting through the bi-directional transmission circuit 20.
Each of the junctions JU is provided to simulate the scattering manner of the air-pressure wave which is scattered at the predetermined portion of the resonance tube, wherein the diameter of the tube is changed at the predetermined portion. As the junction shown in FIG. 15, the four-multiplication-grid-type circuit, containing four multipliers M1 to M4 and adders A1, A2, is employed. Herein, "k+1", "-k", "1-k", "k" described with the multipliers M1 to M4 designate respective multiplication coefficients. The value k is determined such that the transmission characteristic of this junction can well simulate that of the actual resonance tube.
In the circuitry shown in FIG. 15, data P corresponding to the blowing pressure to be applied to the mouthpiece of the wind instrument is applied to both of the adder 12 and subtracter 13. Then, the output data of the adder 12 is transmitted through one line consisting of the delay circuit D, junction JU, another delay circuit D . . . , then, reached at the low-pass filter LPF. Thereafter, this data is transmitted through the low-pass filter LPF and high-pass filter HPF, and then also transmitted backward through another line consisting of the delay circuit D, junction JU, another delay circuit D, . . . . Finally, it is outputted from the bi-directional transmission circuit 20, and then supplied to the subtracter 13.
As described above, the output data of the bil-directional transmission circuit 20 may correspond to the pressure of the air-pressure wave which is reflected by the end terminal of the resonance tube and then returned back to the gap between the mouthpiece and reed. In the subtracter 13, the foregoing data P is subtracted from the output data of the bi-directional transmission circuit 20. As a result of the subtraction performed by the subtracter 13, it is possible to obtain data P1 which corresponds to the air pressure applied to the gap between the mouthpiece and reed. This data P1 is supplied to the nonlinear circuit 11, from which data Y is outputted. This data Y corresponds to the sectional area of the gap formed between the mouthpiece and reed, in other words, the admittance imparted to the air flow. Incidentally, the non-linear circuit 11 stores information of non-linear function A which represents the relationship between the air pressure, applied to the gap between the mouthpiece and reed, and sectional area of the gap. Thus, the input data of the non-linear circuit 11 corresponds to the air pressure, while the output data thereof corresponds to the sectional area.
The above-mentioned data P1 and Y are subjected to the multiplication of the multiplier 14, resulting that data FL is obtained. This data FL corresponds to the volume-flow velocity of the air passing through the gap between the mouthpiece and reed. This data FL is multiplied by a multiplication coefficient G in the multiplier 15. Herein, the multiplication coefficient G is a constant which is determined in response to the tube diameter in the vicinity of the mouthpiece of the wind instrument. In other words, this coefficient G correspond to the resistance to the air flow, or impedance imparted to the air flow. Thus, the multiplier 15 outputs a product between the volume-flow velocity of the air flow, passing through the gap between the mouthpiece and reed, and impedance imparted to the air flow propagated through the tube. In other words, this product of the multiplier 15, i.e., data P2, corresponds to the pressure variation to be occurred in the tube under effect of the air flow passing through the gap. This data P2 and the foregoing data P are added together by the adder 12, of which addition result is supplied to the bi-directional transmission circuit 20.
As described above, the data is circulating through the closed loop configured by the excitation circuit 10 and bi-directional transmission circuit 20, while the resonating operation is performed on the circulating data. Then, the input data of the low-pass filter LPF of the bi-directional transmission circuit 20 is picked up for the synthesis of the musical tone. On the basis of this data, the musical tones are produced.
Meanwhile, the so-called "sub-tone performing technique" is sometimes employed when actually performing the wind instrument. In this sub-tone performing technique, the noise component of the sound which is occurred when blowing the breath into the gap between the mouthpiece and reed of the wind instrument is intentionally exaggerated. Conventionally, such composition of the noise is made by convoluting the noise data with the data P corresponding to the blowing pressure.
When actually blowing the breath into the gap between the mouthpiece and reed of the wind instrument, the turbulent flow is caused at the gap, by which the air-pressure wave is scattered in the tube, resulting that the above-mentioned noise component of the sound may be occurred. However, the conventional noise reproducing method, in which the noise data is merely convoluted with the blowing-pressure data, cannot simulate the actual noise-generating mechanism of the wind instrument with accuracy. For this reason, there is a drawback in that the noise produced by the conventional method may lack the natural characteristic of the noise to be actually generated. In the non-electronic instrument such as the clarinet, the ratio of the noise component included in the sound is relatively high just after the sound is produced, however, it is reduced as the sound level becomes constant. However, the conventional method cannot accurately simulate such variation of the noise component included in the sound to be produced.